King Abdullah's promise that women will finally be allowed to vote is a welcome move away from the discrimination and exclusion that Saudi women have suffered for so long," said Sarah Leah Whitson, Middle East director at Human Rights Watch in a Monday statement.

"Sadly, King Abdullah's promise of reform in 2015 doesn't come soon enough for women to vote in upcoming municipal elections," said Whitson.

The absolute monarch on Sunday granted women the right to vote and run in municipal elections, in an historic first for the ultra-conservative country where women are subjected to many restrictions.

"Starting with the next term, women will have the right to run in municipal elections and to choose candidates, according to Islamic principles," the king said in speech to the Shura Council.

In addition to participating in the only public polls in the country, women would have the right to join the all-appointed Shura (consultative) Council, the king said.

The decision means that women will be able to take part in the elections scheduled in four years time but not in polls due on Thursday as nominations have already closed.

More than 5,000 men will compete in Thursday's municipal elections, only the second in Saudi Arabia's history, to fill half the seats in the kingdom's 285 municipal councils. The other half are appointed by the government.

The first elections were held in 2005, but the government extended the existing council's term for two years.

Women's rights activists have long fought for the right to vote in the Gulf kingdom, which applies a strict version of Sunni Islam and bans women from driving or travelling without the consent of a male guardian.

"In his statement ... Abdullah made no reference to reforming other areas of discrimination against women, such as the guardianship system that authorises male control over women and the ban on women driving," HRW said.

London-based advocacy group Amnesty International has also cautiously welcomed the decision, but said the kingdom was moving much too slowly on women's rights.

"It is a welcome, albeit limited, step along the long road towards gender equality in Saudi Arabia," said Philip Luther, Amnesty's Deputy Director for the Middle East and North Africa.

"It is, however, much overdue and does not go nearly far enough.

"While moving in the right direction, Saudi Arabia is moving far too slowly. Ultimately, it is no great achievement to be one of the last countries in the world to grant women the vote," Luther said.